1. Field of the Invention
The invention generally relates to a semiconductor device and method of manufacture and, more particularly, to a semiconductor having selectively nitrided gate oxides.
2. Background Description
Silicon dioxide has served as the gate insulator of choice for field effect transistors (FETs) for many years. The reason is that silicon dioxide offers a combination of desired properties including good electron and hole mobility, ability to maintain electronic (surface) states at the interface low, relatively low trapping rates of holes and electrons and excellent compatibility with CMOS processing. Typically, a thin gate insulator is desired to better couple and control the electric potential from the gate electrode to the channel.
Concomitantly, continued advancement of integrated circuit technology depends in part on scaling of device dimensions. However, as the thickness of silicon dioxide films decrease with each generation of semiconductor devices, leakage current through the dielectric increases and eventually becomes unacceptable. Additionally, decreased thickness enables penetration of dopants (e.g., boron) from the gate into the gate dielectric, counter doping the channel and thereby degrading performance.
One method that has emerged to reduce these undesirable effects entails introducing nitrogen into gate SiO2. As nitrogen is introduced, the dielectric constant of the gate increases. The introduction of nitrogen substantially reduces boron penetration even at relatively low concentrations. In higher concentrations, introduced nitrogen reduces gate leakage. Unfortunately, high concentrations of nitrogen cause threshold-voltage shifts, particularly on pFETs. Thus, to reduce the adverse impact on pFETs, the maximum nitrogen introduced is limited, at the expense of gate leakage, particularly in nFETs.
The invention is directed to overcoming one or more of the problems as set forth above.